1. Field of the Invention
The field of the invention generally relates to the commercial and industrial production of electrical power and, more particularly, to a system and method for protecting and controlling electric power networks.
2. Description of Related Art
A typical power distribution grid generally includes a power plant, a transmission substation, high voltage transmission lines, and a power substation. The power plant's spinning generator outputs three-phase alternating-current (AC) electrical power, which leaves the generator and enters the transmission substations. Transformers at the transmission substation substantially boost the generator voltage to a high voltage sufficient to transmit the electrical power over long distances via the high voltage transmission lines. Before the transmitted electrical power is used by homes or industry, it passes through a power substation.
A power substation generally includes transformers that step the generator voltages down to distribution voltages; one or more distribution “busses” that split the stepped-down distribution voltages off in multiple directions; and a variety of circuit breakers and disconnect switches that can be configured to disconnect the power substation (or a portion thereof) from the power grid or to disconnect one or more distribution lines from the power substation. In medium voltage to extra-high voltage substations, this primary equipment (e.g., the transformers, circuit breakers, disconnect switches, distribution busses, and the like, that are components of an electrical power substation) is located in an area of the power substation known as the switchyard.
A typical layout of a power substation separates the primary equipment described above from the protection and control equipment that interfaces with and manages it. Thus, while the primary equipment typically resides in the switchyard, the protection and control equipment typically resides in a separate control house.
Examples of protection and control equipment include microprocessor-based protective relays, meters, control switches, remote terminal units, human-machine-interface (“HMI”) terminals, and the like—often referred to as Intelligent Electronic Devices (IEDs). An example of a conventional IED is the Model D25 Multifunction IED for Substation Control manufactured by the General Electric Company of Schenectady, N.Y. This unit monitors voltage difference, phase angle difference, and slip frequency. It also functions as a programmable logic controller, substation local area network node, and an IED gateway. Many IED's communicate using the Supervisory Control and Data Acquisition (SCADA) protocol.
In operation, IED's manage the substation's power output by monitoring data from sensors associated with the primary equipment. To maintain desired voltage levels, IED's are often configured to issue commands to one or more pieces of primary equipment if voltage, current, and/or frequency anomalies are detected. These commands may instruct one or more pieces of primary equipment to operate in a pre-determined manner (e.g., to trip a circuit breaker).
A disadvantage of separating conventional IEDs from their managed pieces of primary equipment is that miles of copper wiring are needed to interconnect the primary equipment with the conventional IEDs. Often, a medium-voltage to high voltage power substation has upwards of tens of thousands of terminations and millions of terminations, respectively, e.g., the connections made when the ends of control cables are attached to termination racks located at the control house. Another disadvantage is the significant cost associated with building or retrofitting such systems, due to the millions of wire terminations involved. The majority of this cost relates to the design, installation, testing, and documentation of the control wiring. International Electrotechnical Commission (“IEC”) Standard 61850 (Communication Networks and Systems in Substations) is a proposed industry-wide basis for automation of power substations in an electric power delivery system. Preliminary approaches at implementing this standard and reducing the impact of copper wiring, however, fail to provide specific teachings or a solid, workable architecture. Such approaches, and the standard itself, leave numerous gaps yet to be filled in. A detailed discussion of the drawbacks associated with IEC 61850 specifically, and the disadvantages associated with prior approaches generally, is provided in a paper by B. Kasztenny, J. Whatley, E. Udren, J. Burger, D. Finney, M. Adamiak, entitled “Unanswered Questions about IEC 61850—What needs to happen to realize the vision?”, Proceedings of the 32nd Annual Western Protective Relay Conference, Spokane, Wash., Oct. 25-27, 2005.
A solution is thus needed that provides a new power substation architecture, new protection and control equipment, and/or a new method of operating a power substation.